Control architecture and method to evaluate engine off operation of a hybrid powertrain system operating in a continuously variable mode

ABSTRACT

There is provided a method and apparatus to determine operating conditions for a powertrain comprising an internal combustion engine and first and second electrical machines and an electro-mechanical transmission selectively operative to transmit torque therebetween. The method comprises determining a torque output and an operating cost for operating the first and second electrical machines of the hybrid transmission effective to meet an operator torque request when the engine is operating in an engine-off operating state. Determining the torque output for operating the first and second electrical machines comprises executing a predetermined system equation effective to determine motor torque outputs from each of the first and second electrical machines based upon the selected parametric value for the input torque and the operator torque request.

TECHNICAL FIELD

This invention pertains generally to control systems for powertrain control systems employing electro-mechanical transmissions.

BACKGROUND OF THE INVENTION

Powertrain architectures comprise torque-generative devices, including internal combustion engines and electric machines, which transmit torque through a transmission device to a vehicle driveline. One such transmission includes a two-mode, compound-split, electro-mechanical transmission which utilizes an input member for receiving motive torque from a prime mover power source, typically an internal combustion engine, and an output member for delivering motive torque from the transmission to the vehicle driveline. Electrical machines, operatively connected to an electrical energy storage device, comprise motor/generators operable to generate motive torque for input to the transmission, independently of torque input from the internal combustion engine. The electrical machines are further operable to transform vehicle kinetic energy, transmitted through the vehicle driveline, to electrical energy potential that is storable in the electrical energy storage device. A control system monitors various inputs from the vehicle and the operator and provides operational control of the powertrain system, including controlling transmission gear shifting, controlling the torque-generative devices, and regulating the electrical power interchange between the electrical energy storage device and the electrical machines.

The exemplary electro-mechanical transmissions are selectively operative in fixed gear modes and continuously variable modes through actuation of the torque-transfer clutches, typically employing a hydraulic circuit to effect clutch actuation. A fixed gear mode occurs when rotational speed of the transmission output member is a fixed ratio of rotational speed of the input member from the engine, typically due to actuation of one or more torque-transfer clutches. A continuously variable mode occurs when rotational speed of the transmission output member is variable based upon operating speeds of one or more electrical machines. The electrical machines can be connected to the output shaft via actuation of a clutch, or by direct connection. Clutch actuation and deactivation is typically effected through a hydraulic circuit.

Engineers implementing powertrain systems having electro-mechanical transmissions are tasked with implementing control schemes to monitor system states and control operation of various systems and actuators to effectively control powertrain operation. Such a system is described hereinafter.

SUMMARY OF THE INVENTION

In accordance with an embodiment of the invention, a method and an apparatus are provided to control operation of a powertrain system comprising a torque transmission device operative to transmit torque input from a plurality of torque-generative devices.

The method is directed to determine operating conditions for a powertrain comprising an internal combustion engine and first and second electrical machines and an electro-mechanical transmission selectively operative to transmit torque therebetween. The method comprises determining an operating cost for operating the first and second electrical machines of the hybrid transmission effective to meet an operator torque request when the engine is operating in an engine-off operating state. The operating costs can be compared to operating costs for other operating states in an optimization routine. Determining the torque output for operating the first and second electrical machines comprises executing a predetermined system equation effective to determine motor torque outputs from each of the first and second electrical machines based upon the selected parametric value for the input torque and the operator torque request.

An aspect of the invention comprises the method intended to be executed in a control system for a hybrid powertrain system including the internal combustion engine and an electro-mechanical transmission. The control system preferably comprises a distributed control module architecture comprising a plurality of signally connected control modules including a hybrid control module, an engine control module, a transmission control module, and, a power inverter control module. The transmission is selectively operative in a plurality of fixed gear modes and continuously variable modes through selective actuation of a plurality of torque-transfer clutches.

These and other aspects of the invention will become apparent to those skilled in the art upon reading and understanding the following detailed description of the embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may take physical form in certain parts and arrangement of parts, an embodiment of which is described in detail and illustrated in the accompanying drawings which form a part hereof, and wherein:

FIG. 1 is a schematic diagram of an exemplary powertrain, in accordance with the present invention;

FIG. 2 is a schematic diagram of an exemplary architecture for a control system and powertrain, in accordance with the present invention;

FIG. 3 is a graphical depiction, in accordance with the present invention;

FIGS. 4-9 are schematic flowcharts, in accordance with the present invention; and,

FIG. 10 is a datagraph, in accordance with the present invention.

DETAILED DESCRIPTION OF AN EMBODIMENT OF THE INVENTION

Referring now to the drawings, wherein the showings are for the purpose of illustrating the invention only and not for the purpose of limiting the same, FIGS. 1 and 2 depict a system comprising an engine 14, transmission 10, control system, and driveline which has been constructed in accordance with an embodiment of the present invention. The control scheme described herein comprises a method to determine operating conditions for a powertrain comprising an internal combustion engine and a hybrid transmission selectively operative to transmit torque therebetween. The method comprises determining an operating cost for operating the electrical machines of the hybrid transmission effective to meet an operator torque request when the engine is operating in an engine-off operating state, effective to meet the operator torque request. The operating cost can be compared to operating costs for other operating states in an optimization routine. An exemplary optimization routine has been described in commonly assigned U.S. Pat. No. 7,568,994, entitled CONTROL ARCHITECTURE FOR SELECTION OF OPTIMAL MODE OR GEAR AND INPUT SPEED FOR A HYBRID POWERTRAIN SYSTEM, which is incorporated herein by reference. Determining torque output for operating the electrical machines comprises executing a predetermined system equation effective to determine motor torque outputs from each of the electrical machines based upon the selected parametric value for the input torque and the operator torque request.

The exemplary hybrid powertrain system is configured to execute the strategic control scheme for controlling the engine depicted in FIGS. 3-9. Mechanical aspects of the exemplary transmission 10 are disclosed in detail in commonly assigned U.S. Pat. No. 6,953,409, entitled “Two-Mode, Compound-Split, Hybrid Electro-Mechanical Transmission having Four Fixed Ratios”, which is incorporated herein by reference. The exemplary two-mode, compound-split, electro-mechanical hybrid transmission embodying the concepts of the present invention is depicted in FIG. 1. The transmission 10 preferably includes a ring gear 80 attached to an input shaft 12 having an input speed, N_(I) that is preferably driven by the internal combustion engine 14, and an output shaft 64 having an output rotational speed, N_(O). The engine 14 has a crankshaft having characteristic speed N_(E) which is operatively connected to the transmission input shaft 12. When a torque converter clutch device (not shown) operatively connects the engine and transmission, the engine speed N_(E) and output torque T_(E) can differ from transmission input speed N_(I) and input torque T_(I).

The transmission 10 utilizes three planetary-gear sets 24, 26 and 28, and four torque-transmitting devices, i.e., clutches C1 70, C2 62, C3 73, and C4 75. An electro-hydraulic control system 42, preferably controlled by transmission control module (‘TCM’) 17, is operative to control actuation and deactivation of the clutches. Clutches C2 and C4 preferably comprise hydraulically-actuated rotating friction clutches. Clutches C1 and C3 preferably comprise comprising hydraulically-actuated stationary devices grounded to the transmission case 68.

There is first electrical machine comprising a motor/generator 56, referred to as MG-A, and a second electrical machine comprising a motor/generator 72, referred to as MG-B operatively connected to the transmission via the planetary gears. Transmission output shaft 64 is operably connected to a vehicle driveline 90 to provide motive output torque, T_(O) to vehicle wheels. Each clutch is preferably hydraulically actuated, receiving pressurized hydraulic fluid from a pump, described below, via an electro-hydraulic control circuit 42.

The transmission 10 receives input torque from the torque-generative devices, including the engine 14 and the MG-A 56 and MG-B 72, and referred to as ‘T_(I)’, ‘T_(A)’, and ‘T_(B)’ respectively, as a result of energy conversion from fuel or electrical potential stored in an electrical energy storage device (ESD) 74. The ESD 74 is high voltage DC-coupled to transmission power inverter module (‘TPIM’) 19 via DC transfer conductors 27. The TPIM 19 is an element of the control system described hereinafter with regard to FIG. 2. The TPIM 19 transmits electrical energy to and from MG-A 56 by transfer conductors 29, and the TPIM 19 similarly transmits electrical energy to and from MG-B 72 by transfer conductors 31. Electrical current is transmitted to and from the ESD 74 in accordance with whether the ESD 74 is being charged or discharged. TPIM 19 includes the pair of power inverters and respective motor control modules configured to receive motor control commands and control inverter states therefrom for providing motor drive or regeneration functionality. Preferably, MG-A 56 and MG-B 72 are three-phase AC machines each having a rotor operable to rotate within a stator that is mounted on a case of the transmission. The inverters comprise known complementary three-phase power electronics devices.

Referring now to FIG. 2, a schematic block diagram of the control system, comprising a distributed control module architecture, is shown. The elements described hereinafter comprise a subset of an overall vehicle control architecture, and are operable to provide coordinated system control of the powertrain system described herein. The control system is operable to synthesize pertinent information and inputs, and execute algorithms to control various actuators to achieve control targets, including such parameters as fuel economy, emissions, performance, driveability, and protection of hardware, including batteries of ESD 74 and MG-A and MG-B 56, 72. The distributed control module architecture includes engine control module (‘ECM’) 23, transmission control module (‘TCM’) 17, battery pack control module (‘BPCM’) 21, and TPIM 19. A hybrid control module (‘HCP’) 5 provides overarching control and coordination of the aforementioned control modules. There is a User Interface (‘UI’) 13 operably connected to a plurality of devices through which a vehicle operator typically controls or directs operation of the powertrain including the transmission 10 through a request for a torque output. Exemplary vehicle operator inputs to the UI 13 include an accelerator pedal, a brake pedal, transmission gear selector, and, vehicle speed cruise control. Each of the aforementioned control modules communicates with other control modules, sensors, and actuators via a local area network (‘LAN’) bus 6. The LAN bus 6 allows for structured communication of control parameters and commands between the various control modules. The specific communication protocol utilized is application-specific. The LAN bus and appropriate protocols provide for robust messaging and multi-control module interfacing between the aforementioned control modules, and other control modules providing functionality such as antilock brakes, traction control, and vehicle stability.

The HCP 5 provides overarching control of the hybrid powertrain system, serving to coordinate operation of the ECM 23, TCM 17, TPIM 19, and BPCM 21. Based upon various input signals from the UI 13 and the powertrain, including the battery pack, the HCP 5 generates various commands, including: an operator torque request (‘T_(O) _(—) _(REQ)’) output to driveline 90, the input torque T_(I) originating from the engine, clutch torque, (‘T_(CL) _(—) _(N)’) for the N various torque-transfer clutches C1, C2, C3, C4 of the transmission 10; and motor torques T_(A) and T_(B) for MG-A and MG-B. The TCM 17 is operatively connected to the electro-hydraulic control circuit 42, including monitoring various pressure sensing devices (not shown) and generating and executing control signals for various solenoids to control pressure switches and control valves contained therein.

The ECM 23 is operably connected to the engine 14, and functions to acquire data from a variety of sensors and control a variety of actuators, respectively, of the engine 14 over a plurality of discrete lines collectively shown as aggregate line 35. The ECM 23 receives the engine torque command from the HCP 5, and generates a desired axle torque, and an indication of actual input torque, T_(I), to the transmission, which is communicated to the HCP 5. For simplicity, ECM 23 is shown generally having bi-directional interface with engine 14 via aggregate line 35. Various other parameters that may be sensed by ECM 23 include engine coolant temperature, engine input speed, N_(E), to shaft 12 which translates to transmission input speed, N_(I), manifold pressure, ambient air temperature, and ambient pressure. Various actuators that may be controlled by the ECM 23 include fuel injectors, ignition modules, and throttle control modules.

The TCM 17 is operably connected to the transmission 10 and functions to acquire data from a variety of sensors and provide command signals to the transmission. Inputs from the TCM 17 to the HCP 5 include estimated clutch torques (T_(CL) _(—) _(EST) _(—) _(N)) for each of the N clutches C1, C2, C3, and, C4 and transmission output rotational speed N_(O) of shaft 64. Other actuators and sensors may be used to provide additional information from the TCM to the HCP for control purposes. The TCM 17 monitors inputs from pressure switches and selectively actuates pressure control solenoids and shift solenoids to actuate various clutches to achieve various transmission operating modes, as described hereinbelow.

The BPCM 21 is signally connected one or more sensors operable to monitor electrical current or voltage parameters of the ESD 74 to provide information about the state of the batteries to the HCP 5. Such information includes battery state-of-charge, battery voltage and available battery power, referred to as a range P_(BAT) _(—) _(MIN) to P_(BAT) _(—) _(MAX).

Each of the aforementioned control modules is preferably a general-purpose digital computer generally comprising a microprocessor or central processing unit, storage mediums comprising read only memory (ROM), random access memory (RAM), electrically programmable read only memory (EPROM), high speed clock, analog to digital (A/D) and digital to analog (D/A) circuitry, and input/output circuitry and devices (I/O) and appropriate signal conditioning and buffer circuitry. Each control module has a set of control algorithms, comprising resident program instructions and calibrations stored in ROM and executed to provide the respective functions of each computer. Information transfer between the various computers is preferably accomplished using the aforementioned LAN 6.

Algorithms for control and state estimation in each of the control modules are typically executed during preset loop cycles such that each algorithm is executed at least once each loop cycle. Algorithms stored in the non-volatile memory devices are executed by one of the central processing units and are operable to monitor inputs from the sensing devices and execute control and diagnostic routines to control operation of the respective device, using preset calibrations. Loop cycles are typically executed at regular intervals, for example each 3.125, 6.25, 12.5, 25 and 100 milliseconds during ongoing engine and vehicle operation. Alternatively, algorithms may be executed in response to occurrence of an event.

The exemplary two-mode, compound-split, electro-mechanical transmission operates in several fixed gear operating modes and continuously variable operating modes, described with reference to FIG. 1, and Table 1, below.

TABLE 1 Transmission Operating Range State Actuated Clutches Mode 1 - Engine Off (M1_Eng_Off) C1 70 Mode 1 - Engine On (M1_Eng_On) C1 70 Fixed Ratio 1 (GR1) C1 70 C4 75 Fixed Ratio 2 (GR2) C1 70 C2 62 Mode 2 - Engine Off (M2_Eng_Off) C2 62 Mode 2 - Engine On (M2_Eng_On) C2 62 Fixed Ratio 3 (GR3) C2 62 C4 75 Fixed Ratio 4 (GR4) C2 62 C3 73

The various transmission operating range states described in the table indicate which of the specific clutches C1, C2, C3, and C4 are engaged or actuated for each of the operating range states. A first mode, i.e., Mode 1, is selected when clutch C1 70 is actuated in order to “ground” the outer gear member of the third planetary gear set 28. The engine 14 can be either on or off. A second mode, i.e., Mode 2, is selected when clutch C1 70 is released and clutch C2 62 is simultaneously actuated to connect the shaft 60 to the carrier of the third planetary gear set 28. Again, the engine 14 can be either on or off. For purposes of this description, Engine Off is defined by engine input speed, N_(E), being equal to zero revolutions per minute (RPM), i.e., the engine crankshaft is not rotating. Other factors outside the scope of the invention affect when the electrical machines 56, 72 operate as motors and generators, and are not discussed herein.

The control system, shown primarily in FIG. 2, is operable to provide a range of transmission output speeds at shaft 64 from relatively slow to relatively fast within each operating range state. The combination of two modes with a slow-to-fast output speed range in each range state allows the transmission 10 to propel a vehicle from a stationary condition to highway speeds, and meet various other requirements as previously described. Additionally, the control system coordinates operation of the transmission 10 so as to allow synchronized shifts between the modes.

The first and second modes of operation refer to circumstances in which the transmission functions are controlled by one clutch, i.e., either clutch C1 62 or C2 70, and by the controlled speed and torque of the electrical machines 56 and 72, which can be referred to as a continuously variable transmission mode. Certain ranges of operation are described below in which fixed gear ratios are achieved by applying an additional clutch. This additional clutch may be clutch C3 73 or C4 75, as shown in the table, above.

When the additional clutch is applied, fixed ratio operation of input-to-output speed of the transmission, i.e., N_(I)/N_(O), is achieved. The rotations of machines MG-A and MG-B 56, 72 are dependent on internal rotation of the mechanism as defined by the clutching and proportional to the input speed measured at shaft 12. The machines MG-A and MG-B function as motors or generators. They are independent of engine to output power flow, thereby enabling both to be motors, both to function as generators, or any combination thereof. This allows, for instance, during operation in Fixed Ratio 1 that motive power output from the transmission at shaft 64 is provided by power from the engine and power from MG-A and MG-B, through planetary gear set 28 by accepting power from ESD 74.

Referring now to FIG. 3, various transmission operating modes are plotted as a function of transmission output speed, N_(O), and transmission input speed, N_(I) for the exemplary powertrain control system shown in FIGS. 1 and 2. The Fixed Ratio operation is shown as individual lines for each of the specific gear ratios, GR1, GR2, GR3, and GR4, as described with reference to Table 1, above. The continuously variable Mode operation is shown as ranges of operation for each of Mode 1 and Mode 2. The transmission operating range state is switched between Fixed Ratio operation and continuously variable Mode operation by activating or deactivating specific clutches. The control system is operative to determine a specific transmission operating mode based upon various criteria, using algorithms and calibrations executed by the control system, and is outside the scope of this invention. Selection of the operating range state of the transmission depends primarily on the operator torque request T_(O) _(—) _(REQ) and the ability of the powertrain to meet that output torque request.

Referring to Table 1 and again to FIG. 3, the low range operating state includes selective actuation of clutches C2, C1, and C4, facilitating operation in any one of continuously variable Mode 1, and fixed gears GR1, and GR2. The high range operating state includes selective actuation of clutches C2, C3, and C4, facilitating operation in any one of continuously variable Mode 2 and fixed gears GR3 and GR4. The ranges of continuously variable operation for Mode 1 and Mode 2 can overlap.

In response to an operator's action, as captured by the UI 13, the supervisory HCP control module 5 and one or more of the other control modules determine the operator torque request T_(O) _(—) _(REQ), to be executed at shaft 64. Final vehicle acceleration is affected by other factors, including, e.g., road load, road grade, and vehicle mass. The operating mode is determined for the exemplary transmission based upon a variety of operating characteristics of the powertrain. This includes an operator demand for torque, typically communicated through inputs to the UI 13 as previously described. Additionally, a demand for output torque is predicated on external conditions, including, e.g., road grade, road surface conditions, or wind load. The operating mode may be predicated on a powertrain torque demand caused by a control module command to operate of the electrical machines in an electrical energy generating mode or in a torque generating mode. The operating mode can be determined by an optimization algorithm or routine operable to determine optimum system efficiency based upon operator demand for power, battery state of charge, and energy efficiencies of the engine 14 and MG-A and MG-B 56, 72. The control system manages torque inputs from the engine 14 and MG-A and MG-B 56, 72 based upon an outcome of the executed optimization routine, and system optimization occurs to optimize system efficiencies to improve fuel economy and manage battery charging. Furthermore, operation can be determined based upon a fault in a component or system. The HCP 5 monitors the parametric states of the torque-generative devices, and determines the output of the transmission required to arrive at the desired torque output, as described hereinbelow. Under the direction of the HCP 5, the transmission 10 operates over a range of output speeds from slow to fast in order to meet the operator demand.

Referring now to FIGS. 4-10, controlling operation of a hybrid powertrain is described, with reference to the exemplary powertrain described in FIGS. 1, 2, and 3. Referring specifically to FIG. 4, the method and system described herein comprise an aspect of strategic control optimization (Block 110), wherein a preferred or desired operating range state (Op_Range_(DES)) is selected based primarily upon output speed, N_(O) of shaft 64 and the operator torque request, T_(O) _(—) _(REQ). Output of the strategic control includes the preferred or desired operating range state (‘Op_Range_(DES)’) and desired input speed (‘N_(I) _(—) _(DES)’) each which are input to a shift execution control block 120. Other aspects of the overall architecture for strategic optimization and control of the exemplary powertrain are described in commonly assigned U.S. Pat. No. 7,691,026, entitled CONTROL ARCHITECTURE FOR OPTIMIZATION AND CONTROL OF A HYBRID POWERTRAIN SYSTEM which is incorporated by reference, and need not be described herein.

The method comprises determining operating conditions for the exemplary powertrain, comprising determining a torque output and an operating cost for operating the first and second electrical machines of the hybrid transmission effective to meet an operator torque request when the engine is operating in an engine-off operating state. Determining the torque output for operating the first and second electrical machines comprises executing a predetermined system equation effective to determine motor torque outputs from each of the first and second electrical machines based upon the selected parametric value for the input torque and the operator torque request.

In overall operation, the method includes monitoring output of the transmission, typically N_(O), the operator torque request, T_(O) _(—) _(REQ), at shaft 64, and, the available battery power P_(BAT) _(—) _(MIN) and P_(BAT) _(—) _(MAX). A torque range or torque value for each of the allowable range states is determined. A cost for operating in each of the determined torque ranges is calculated, and one of the determined torque ranges is selected as a preferred operating range state based upon the calculated costs for each determined torque range. The powertrain can be controlled to the preferred operating range state thereafter.

Referring now to FIG. 5, a functional block diagram details the strategic control block 110 of FIG. 4, and depicts inputs N_(O) and T_(O) _(—) _(REQ) to a strategic manager segment 220, which has outputs to a system constraint segment 240 and an optimization segment 260. The output of the system constraint segment 240 is input to the optimization segment 260. The outputs of the optimization segment 260 are input to the shift stabilization and arbitration segment 280, which has an output comprising the preferred operating range state, OP_Range_(DES) and desired input speed, N_(I) _(—) _(DES).

Referring now to FIG. 6, the strategic manager segment 220 includes operator inputs, typically torque requests and other inputs through the UI 13, cost structure information, described hereinbelow, and raw strategic inputs, comprising raw signals related to the hybrid powertrain operating conditions, including those related to the ESD 74. Outputs from the strategic manager segment 220 comprise cost structure information (COST), strategic inputs including transmission output speed N_(O), range of available battery power P_(BAT) _(—) _(MIN) and P_(BAT) _(—) _(MAX), and the operator torque request T_(O) _(—) _(REQ).

Referring now to FIG. 7, a detailed description of the strategic system constraints segment 240 is now described. The output speed N_(O) is input to strategic speed constraint segment 230. The speed constraint segment 230 determines minimum and maximum input speeds for operating in each continuously variable mode, i.e., N_(I) _(—) _(MIN) _(—) M1, N_(I) _(—) _(MAX) _(—) M1, N_(I) _(—) _(MIN) _(—) M2, and N_(I) _(—) _(MAX) _(—) M2. The minimum and maximum input speeds, the available battery power P_(BAT) _(—) _(MIN) and P_(BAT) _(—) _(MAX), and the operator torque request T_(O) _(—) _(REQ) are output to strategic system constraints segment 250 which determines the inputs to the strategic optimization segment 260 for each of the hybrid operating range states, i.e., GR1, GR2, GR3, GR4, M1_Eng_Off, M1_Eng_On, M2_Eng_Off, and M2_Eng_On, based upon current operating constraints, specifically output speed N_(O). There are three output paths 242, 244, 246 from segment 250 which supply inputs to optimization segment 260. Specifically, output path 246 provides relevant system constraint information when the engine is off, i.e., not rotating, comprising an input speed, N_(I)=0 and an input torque T_(I)=0, indicative of system operation comprising Mode 1-Engine Off operation (M1_Eng_Off) and Mode 2-Engine Off operation (M2_Eng_Off). This information is communicated to each of segments 266 and 268 of segment 260.

Referring now to FIG. 8, the strategic optimization segment 260 is now described. The allowable hybrid operating range states output from segment 240 to the strategic optimization segment 260 are used to identify which of the optimization segments 262, 264, 266, 268, 270, 272, 274 and 276 are to be executed. Segments 262, 264, 266, 268, 270, 272, 274 and 276 each comprise optimization segments, wherein an optimum operating cost (P_(COST)) is determined for each of the permissible operating range states, based upon the inputs previously described, including the previously described range of torque values and costs related to driveability, fuel economy, emissions, and battery life. The optimum operating cost preferably comprises a minimum operating cost at a powertrain operating point within the range of attainable torque values for each operating range state.

Referring now to FIGS. 9 and 10, a method to determine preferred operating conditions for operating the exemplary powertrain in either of Mode 1 or Mode 2 with the engine off is described. The engine off operating mode is identified as Point A on the datagraph depicted in FIG. 10. The input torque value to the transmission and driveline comprising input torque of zero T_(I)=0, is input from segment 246 to segment 260 for each of blocks 266 and 268. Parametric values for transmission input torque (T_(I)=0) is input to system equation 362, from which parametric values for MG-A torque (T_(A)) and MG-B torque (T_(B)) are determined. The motor torques T_(A) and T_(B) and input torque T_(I)=0 are input to a cost function 364, which calculates a cost (P_(COST)) for operating the exemplary powertrain to achieve the specific parametric input torque and motor torque. The costs are output to block 280 from each of blocks 266 and 268, and comprise costs associated with operating the powertrain with the engine off to achieve the desired output torque, T_(O).

The parametric values of input torque T_(I)=0 and input speed N_(I)=0 are input to system equation 362, through line 246 for either of Mode 1 and Mode 2 to segment 260, which comprises an element of either of segments 266 for Mode 1 and segment 268 for Mode 2, and comprise an output from segment 240, described above. When the exemplary transmission is operated in one of the continuously variable modes Mode 1 or Mode 2, the speed relationship between MG-A, MG-B, N_(I) and N_(O) is defined as shown in Eq. 1, below:

$\begin{matrix} {\begin{bmatrix} N_{A} \\ N_{B} \end{bmatrix} = {\begin{bmatrix} b_{11} & b_{12} \\ b_{21} & b_{22} \end{bmatrix}\begin{bmatrix} N_{I} \\ N_{O} \end{bmatrix}}} & \lbrack 1\rbrack \end{matrix}$ wherein N_(I)=0 comprises the input speed from engine 14, N_(O) is the transmission output speed, N_(A) and N_(B) are the operating speeds for MG-A 56 and MG-B 72, and b₁₁, b₁₂, b₂₁, b₂₂, are known scalar values determined for the specific application in the specific operating range state. Therefore, the determined scalar values for b₁₁, b₁₂, b₂₁, b₂₂ are specific to each of Mode 1 and Mode 2. In this application, when the transmission output speed, N_(O) is known, and N_(I)=0, motor speeds N_(A) and N_(B) can be determined.

The torque relationship between MG-A, MG-B, N_(I) and N_(O) is defined as shown in Eq. 2, below:

$\begin{matrix} {\begin{bmatrix} T_{A} \\ T_{B} \end{bmatrix} = {\begin{bmatrix} d_{11} & d_{12} & d_{13} & d_{14} \\ d_{21} & d_{22} & d_{23} & d_{24} \end{bmatrix}\begin{bmatrix} T_{I} \\ T_{O} \\ {\overset{\bullet}{N}}_{I} \\ {\overset{\bullet}{N}}_{O} \end{bmatrix}}} & \lbrack 2\rbrack \end{matrix}$ wherein T_(I)=0 is the input torque from engine 14, T_(O) is the transmission output torque, T_(A) and T_(B) are the operating torques for MG-A 56 and MG-B 72, {dot over (N)}_(I) and {dot over (N)}_(O) represent time-rate changes in input speed and output speed of the engine 14, and d₁₁, d₁₂, d₁₃, d₁₄, d₂₁, d₂₂, d₂₃, d₂₄ are known scalar values determined for each operating range state, i.e., either of Mode 1 and Mode 2, of the application. In this application, when the transmission output torque T_(O) is substantially equal to the operator torque request T_(O) _(—) _(REQ), and T_(I)=0 for the engine 14, and thus T_(A) and T_(B) can be determined.

The system equation (Block 362) derived from Eqs. 1 and 2, provides the motor values for MG-A and MG-B is as follows in Eq. 3:

$\begin{matrix} {\begin{bmatrix} T_{A} \\ T_{B} \end{bmatrix} = {{\begin{bmatrix} a_{11} & a_{12} \\ a_{21} & a_{22} \end{bmatrix}\begin{bmatrix} T_{i} \\ T_{o} \end{bmatrix}} + \begin{bmatrix} b_{1} \\ b_{2} \end{bmatrix}}} & \lbrack 3\rbrack \end{matrix}$ wherein a₁₁, a₁₂, a₂₁, a₂₂, b₁, and b₂ are known scalar values determined for the specific application, and for the specific mode of operation, i.e., Mode 1 or Mode 2.

The calculated parametric values for motor torques T_(A) and T_(B) which are output from Eq. 3 are input to the cost function (Block 364) to calculate a cost, P_(COST), which is associated with the selected parametric values for T_(I)=0 and N_(I)=0.

The cost information used in the cost function 364 preferably comprises operating costs which are generally determined based upon factors related to vehicle driveability, fuel economy, emissions, and battery life for the determined torque range. Furthermore, costs in this invention are assigned and associated with only electrical power consumption associated with a specific operating point of the powertrain system for the vehicle. Lower operating costs are generally associated with lower battery power usage, and lower emissions for an operating point, and take into account a current operating range state of the powertrain system. The optimum operating cost (P_(COST)) can be determined by calculating a total powertrain system loss, comprising an overall system power loss and a cost penalty, such as can be associated with controlling battery state of charge. The overall system power loss comprises a term based upon losses in the electrical system (e.g. wire impedances and switching and solenoid losses), and heat losses. Other losses include electrical machine power losses and internal battery power losses. Other factors may also be considered, including factors related to battery life due to depth of discharge of the ESD 74, current ambient temperatures and their effect on state of charge of the battery. Operating costs are preferably developed relative to specific powertrain/vehicle applications during vehicle calibration pre-production. An exemplary method for determining engine power losses are described in commonly assigned U.S. Pat. No. 7,149,618 B2 entitled COST STRUCTURE METHOD INCLUDING FUEL ECONOMY AND ENGINE EMISSION CONSIDERATIONS, the contents of which are incorporated herein by reference.

It is understood that modifications in the hardware are allowable within the scope of the invention. The invention has been described with specific reference to the embodiments and modifications thereto. Further modifications and alterations may occur to others upon reading and understanding the specification. It is intended to include all such modifications and alterations insofar as they come within the scope of the invention. 

1. Method for operating a powertrain comprising an internal combustion engine and first and second electrical machines and an electro-mechanical transmission configured to transmit torque therebetween, the method comprising monitoring an operator torque request and a present transmission output speed; calculating a first set of motor torques output from the first and second electrical machines corresponding to operating the electromechanical transmission in a first continuously variable mode with the engine in an engine-off operating state in response to the operator torque request and the present transmission output speed; calculating a second set of motor torques output from the first and second electrical machines corresponding to operating the electromechanical transmission in a second continuously variable mode with the engine in the engine-off operating state in response to the operator torque request and the present transmission output speed; calculating a first operating cost associated with the first set of motor torques output from the first and second electrical machines; calculating a second operating cost associated with the second set of motor torques output from the first and second electrical machines; selecting one of the first and second continuously variable modes as a preferred operating mode based upon the first and second operating costs; and controlling the powertrain in the preferred operating mode with the engine in the engine-off operating state in response to the operator torque request and the present transmission output speed.
 2. The method of claim 1, wherein calculating the first set of motor torques output from the first and second electrical machines corresponding to operating the electromechanical transmission in the first continuously variable mode with the engine in the engine-off operating state in response to the operator torque request and the present transmission output speed comprises executing a predetermined system equation to determine motor torque outputs from each of the first and second electrical machines based upon the operator torque request.
 3. The method of claim 1, wherein the engine-off operating state comprises an engine crankshaft speed being zero revolutions per minute.
 4. Apparatus, comprising: a distributed control module architecture comprising: a plurality of control modules adapted to control operation of a hybrid powertrain; the hybrid powertrain comprising an internal combustion engine and first and second electrical machines and an electro-mechanical transmission configured to transmit torque therebetween; the transmission selectively operative in one of first and second continuously variable operating modes through selective actuation of a plurality of torque-transfer clutches; and, the control modules configured to execute machine code stored therein, the machine code comprising: code to monitor an operator torque request, a present transmission output speed and available battery power; identify at least one permissible powertrain operating range state comprising an engine-off state; determine torque outputs from the first and second electrical machines to achieve a powertrain torque output to meet the operator torque request when the powertrain is operating in the permissible powertrain operating range state comprising the engine-off state; determine an operating cost for operating the first and second electrical machines to achieve the powertrain torque output to meet the operator torque request in the permissible powertrain operating range state comprising the engine-off state, the operating cost associated with the present transmission output speed and the available battery power; select the permissible powertrain operating range state comprising the engine-off state based upon the operating costs; and control the powertrain in the permissible powertrain operating range state comprising the engine-off state to meet the operator torque request.
 5. The apparatus of claim 4, wherein the electro-mechanical transmission comprises a two-mode, compound split transmission selectively operative in one of the first and second continuously variable operating modes through selective actuation of one of the torque-transfer clutches.
 6. The apparatus of claim 5, further comprising the electro-mechanical transmission operative in the first continuously variable operating mode through selective actuation of a first one of the torque-transfer clutches.
 7. The apparatus of claim 5, further comprising the electro-mechanical transmission operative in the second continuously variable operating mode through selective actuation of a second one of the torque-transfer clutches.
 8. Method for operating a powertrain comprising an internal combustion engine and first and second electrical machines and an electro-mechanical transmission selectively operative to transmit torque therebetween, the method comprising: monitoring an operator torque request, a present transmission output speed and available battery power; identifying at least one permissible powertrain operating range state comprising an engine-off state; determining torque outputs from the first and second electrical machines to achieve a powertrain torque output to meet the operator torque request when the powertrain is operating in the permissible powertrain operating range state comprising the engine-off state; determining an operating cost for operating the first and second electrical machines to achieve the powertrain torque output to meet the operator torque request in the permissible powertrain operating range state comprising the engine-off state, the operating cost associated with the present transmission output speed and the available battery power; selecting the permissible powertrain operating range state comprising the engine-off state based upon the operating costs; and, controlling the powertrain in the engine-off state to meet the operator torque request.
 9. The method of claim 8, wherein the permissible powertrain operating range state comprising the engine-off state further comprises a powertrain operating range state comprising one of a first and a second continuously variable operating mode.
 10. The method of claim 8, wherein controlling the powertrain in the engine-off state comprises: selectively actuating one of a plurality of torque-transfer clutches and deactivating the engine to achieve the engine-off state to transmit torque from the electric machines to substantially meet the operator torque request.
 11. The method of claim 10, wherein the engine-off state comprises an engine crankshaft speed being zero revolutions per minute. 